This invention relates to molecular beam epitaxy (MBE) on channeled substrates and, more particularly, to the use of the technique to fabricate mesa geometry semiconductor devices such as stripe geometry junction lasers.
The stripe geometry junction laser was first proposed by R. A. Furnanage and D. K. Wilson (U.S. Pat. No. 3,363,195 issued on Jan. 9, 1968) as a means to reduce the number of lasing modes. The stripe geometry also reduces the threshold current for lasing, which alleviates heat sinking and other problems, and limits the spatial width of the output beam, which facilitates coupling into an optical fiber. Since that early proposal, numerous laser configurations have been devised to implement the stripe geometry concept, but clearly the front runner, both in terms of widespread usage as well as reliability, is the proton bombarded double heterostructure (DH) laser described by J. C. Dyment et al, Applied Physics Letters, Vol. 10, page 84 (1967), and L. A. D'Asaro et al, U.S. Pat. No. 3,824,133 issued on July 16, 1974.
Notwithstanding the success of DH stripe junction lasers delineated by proton bombardment, workers in the art have suggested a virtual plethora of alternative structures aimed primarily at one or more objects such as lowering the lasing threshold, controlling filamentary light outputs and producing more symmetric light beams. One such configuration is the mesa stripe geometry laser. T. Tsukada et al, Applied Physics Letters, Vol 20, page 344 (1972) fabricate such a laser by LPE growth of a double heterostructure, chemically etching a mesa stripe, coating the side walls of the mesa with a silicon phosphate glass film and then depositing a metal contact on the entire upper surface. Similarly, R. A. Logan et al, U.S. Pat. No. 3,833,435 issued on Sept. 3, 1974, subject an LPE GaAs-AlGaAs heterostructure to a slow Br.sub.2 -methanol etch to form a stripe mesa and then regrow AlGaAs by LPE or MBE. Alternatively, Logan et al describe a self-masking structure in which, after the Br.sub.2 -methanol etch, the GaAs active region is selectively etched to undercut the cladding layers and form a pedestal-like mesa. Direct deposition of a metallic contact is then made without shorting the junction in the active region.
Others have reversed the process of chemical etching and LPE growth to fabricate what have been termed embedded epitaxy heterostructures. Thus, for example, I. Samid and C. P. Lee et al, Applied Physics Letters, Vol. 27, page 405 (1975), used an Al.sub.2 O.sub.3 mask and a Br.sub.2 -methanol preferential etch to form [011] oriented channels in a (100) GaAs substrate and then grew Al.sub..4 Ga.sub..6 As-GaAs-Al.sub..4 Ga.sub..6 As-GaAs by LPE in the channels. In a later paper, Applied Physics Letters, Vol. 29, page 365 (1976), the same authors report an improved version of embedded heterostructure LPE lasers using a native oxide mask and H.sub.2 SO.sub.4 :H.sub.2 O.sub.2 :H.sub.2 O (5:1:1) to etch channels in the [011] direction.